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2005 Ford Focus: electrical problems..The alternator..blew..amp fuse

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I have a 2005 Ford Focus with electrical problems. The alternator was replaced by a friend about 2 months ago. At the time the individual blew the 175 amp fuse in line between the alternator and the starter (I think). He replaced that as well. The battery is also new. A few weeks ago we had a check gas cap light and then a check engine light. Now the interior lights on the clock and radio are dimming when the headlights run and the car is puttering at stops. I pulled the battery and checked it, it was fully charged. I haven't checked the alternator except to unplug the neg cable while the car was running. The car continues to run but begins sputtering intermittently. We have also noticed poor gas mileage in the last two weeks. Any suggestions? The belt seems to be in good shape as well, there is no corrosion on the battery, and the connections are tight.
Submitted: 6 years ago.
Category: Ford
Expert:  Chris (aka- Moose) replied 6 years ago.

Hello Dunnyboacter


I'm Chris, Thanks for allowing me to help you here on Just Answer.


I need to know some voltages

  1. With the vehicle off and haveing been off for 30 minutes whats the battery voltage_____?
  2. Now turn on the headlights with the engine still off and let them run for 1 minute then back off, now wait 5 minutes and tell me what the battery voltage is________?
  3. Now star tthe car and turn off all electrical accessories and tell me the voltage at the battery _________?
  4. Now while still idling turn on the headlights and wipers and blower on high and tell me the battery voltage_______?
Customer: replied 6 years ago.
Thank you Chris, but I need to purchase a volt meter before I can answer your questions. Once I've done so I will reply here.
Expert:  Chris (aka- Moose) replied 6 years ago.
Hear from you then, make sure its digital and can do DC volts.
Customer: replied 6 years ago.
1. 12.1V

2. 12.0V

3. 13.4V

4. 13.9V

Expert:  Chris (aka- Moose) replied 6 years ago.

A good battery will have 12.4-12.6 volts. So getting a reading of 12.1 and then 12.0 means the battery is discharged quite a bit. Meaning it only has about 50% of the amps it claims to have. Since the voltage dropped on the light test this means the reserve capacity is also struggling since the battery has very low power. With a battery this low you should be seeing charging voltages more near 14-14.8. The voltages as they are are fine but not with a battery showing this voltage. In this case you first off need to get a long battery charge on it to get this battery back up to health and see why this alternator is not working up to par.

This chargeing system is computer controlled (PCM) so you need to get a good scan tool on it to see what the computer is commanding commpared to what the alternator is putting out. I feel your looking at a alternator which is just not a good one and cant handle the needed output.

Chris (aka- Moose), Technician
Category: Ford
Satisfied Customers: 43515
Experience: 16 years experience
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Category: Ford
Satisfied Customers: 43515
Experience:  16 years experience
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